3 jaw and 4 jaw Chuck sizes

[mksj]

Scroll engagement half or more of the teeth engaged, on an 8" chuck that is 3-4 teeth.

Extending the outer jaws past the edge of the chuck - how far before unsafe?

I have a 6" four jaw chuck for my G0752/G0602. Just bought an 8" diameter disc 0.8" thick of 6061 to make a fixture plate for a recently purchased rotary table. How many threads of engagement should I have in each jaw? The jaws look far enough out that I'm wondering how safe it is. Obviously...

www.hobby-machinist.com

On a 1236 lathe with an 8" chuck, you may be more limited also due to limited swing of the lathe. As an everyday chuck on this size lathe I would be happier using a 6" scroll, switching to a 4J independent for larger diameter or irregular work.

 

[pontiac428]

Heavy chucks start and stop slower, but more rotating mass stabilizes vibrations among other benefits. Just sayin'.

 

[Just for fun]

Thanks for the info. I've only ran across one time I thought a bigger chuck would be nice, even at that it wasn't necessary. I just kind of want one of the ultra-precision chucks that Precession Matthew sales, I was just curious why not an 8". The extra mass weight and maybe limited swing all makes since, and the extra $300 bucks is nothing to sneeze about either.

When the time comes, I'll just get another 6"

 

[pontiac428]

Thanks for the info. I've only ran across one time I thought a bigger chuck would be nice, even at that it wasn't necessary. I just kind of want one of the ultra-precision chucks that Precession Matthew sales, I was just curious why not an 8". The extra mass weight and maybe limited swing all makes since, and the extra $300 bucks is nothing to sneeze about either.

When the time comes, I'll just get another 6"

When it comes time to buy, you won't be confined to either 6" or 8". Most of the european metric chucks are made in 'tweener sizes. Pratt-Burnerd England and Bison, etc. make them in the 7" range. I'd love to run a 6" 6-jaw again, but that has to be the worst size out there to adapt to D1-6, unless the bolts are way inboard.

 

[mickri]

You can never have too many chucks. I have 8 for my craftsman 12x36. Two 8" 4 jaws. A 6" 4 jaw and a 6" 3 jaw. A 5" 3 jaw and a 3" 3 jaw. Plus a ER32 chuck and a Jabsco drill chuck. My next chuck will be an 8" 3 jaw. I keep searching but haven't found one at a price I am willing to pay. So it doesn't matter what you buy now because you will be buying more in the future.

 

[Mtnmac]

Here's a photo of a 8" chunk of aluminum in a 8" 4 jaw chuck on a 12 x 36 lathe. It worked fine, but would not swing over the cross slide. Notice how I have the tool mounted to turn the OD.

 

[verbotenwhisky]

I have chucks from 6"-12.5" and while I really like my 6" set tru type 6 jaw, I don't think a 6 jaw in the 6" range is a great bargain. They are expensive, the jaws tend to be more delicate, and as Mark has aid, they accumulate crud. I have a 6" and a 10" combo Bison and they are also expensive but probably a better value than a 6 jaw as they are more versatile. I particularly like that i can set the stock in the four jaw and then loosen each jaw and slip a soft shim in and then dial in like an independent chuck but still use it as a scroll 90% of the time. You want a stout spindle as the work is a long ways from the bearings and that causes some stress although you don't take heavy cuts with a 12x36 machine. A regular independent chuck is much lighter and easier on the machine, a little tougher on the operator.

Also keep in mind that in your chuck bolts from the front, you don't really need a set tru as you can adjust the plate enough without the set screws and then bolt it down hard.

Finally, in a larger chuck like my 12", a 6 jaw is a joy to use and my favorite.

Dave

If I were to buy a 6 jaw chuck I would want an 8", but I am not ready to get off my wallet yet. I have a E40 collet chuck which I like for small work.

 

[verbotenwhisky]

Here's a photo of a 8" chunk of aluminum in a 8" 4 jaw chuck on a 12 x 36 lathe. It worked fine, but would not swing over the cross slide. Notice how I have the tool mounted to turn the OD.View attachment 461370

I have worked with a 8 1/4" stainless part with my PM1236, I had to rotate the compound out and adjust the tool holder but it wasn't the max I could have turned and I had the tool in the other position parallel to the face of the work and the piece I was working with was only 2" thick. No, the cross slide did not go under it.

 

[verbotenwhisky]

This is a piece of Aluminum from a project I am currently working on, as you can see it is 8 3/4" diameter (started off at 8 7/8" diameter) and it is 2" thick. I used my 8" 4 jaw to turn this and the bottom has been faced as well.